1. Field of the Invention
The present invention relates to an overlock sewing machine, and in particular, to an overlock sewing machine having an upper knife which cuts a cloth end edge onto which over-edge darning is performed.
2. Related Art
For example, in an overlock sewing machine, an over-edge chain stitching is applied onto the cloth end edge while cutting a cloth end edge by an upper knife which moves up and down so as to interlock with a sewing machine main shaft.
Then, in a case where this upper knife is not used, an overlock sewing machine in which the upper knife is withdrawn from a cloth edge cutting position by stopping the upper knife on the lower side of the throat plate, that makes it easy to handle cloth on the throat plate has been known (refer to JP-A-2005-168939, for example). In this sewing machine, biasing means for biasing the upper knife always to the lower side of the throat plate is provided, and when the power transmission with a sewing machine main shaft is cut off in order to stop the upper knife, the upper knife is withdrawn to the lower side of the throat plate by the biasing force of the biasing means.